[LeetCode] 38. Count and Say_Easy
2018-08-11 05:13 Johnson_强生仔仔 阅读(176) 评论(0) 编辑 收藏 举报The count-and-say sequence is the sequence of integers with the first five terms as following:
1. 1 2. 11 3. 21 4. 1211 5. 111221
1
is read off as "one 1"
or 11
.11
is read off as "two 1s"
or 21
.21
is read off as "one 2
, then one 1"
or 1211
.
Given an integer n, generate the nth term of the count-and-say sequence.
Note: Each term of the sequence of integers will be represented as a string.
Example 1:
Input: 1 Output: "1"
Example 2:
Input: 4 Output: "1211"
1. Constraints
1)n >= 1 edge case n == 1: return '1'
2. Ideas
recursive helper() , helper()是一个能count and say 之前的string
3. Code
class Solution(object): def countAndSay(self, n): """ :type n: int :rtype: str """ def helper(n, s): if n == 1: return s pre, i , temp, count = s[0], 0, "", 0 while i < len(s): if s[i] == pre: count += 1 else: temp += str(count) + pre count = 1 pre = s[i] i += 1 if i == len(s): temp += str(count) +pre return helper(n-1, temp) ans = "" return helper(n, '1')